Re: [RFC/PATCH] Make powerpc64 use __thread for per-cpu variables

Alan Modra
2006-05-11T02:01:28Z

On Thu, May 11, 2006 at 11:21:15AM +1000, Paul Mackerras wrote:
> Alan Modra writes:
>
> > gcc shouldn't think there is any reason to cache the address.
>
> Can I rely on that being true in the future?

It isn't true in the *present*, except with a compiler on my home
machine. :-)

__thread int i1;
void
f3 (void)
{
int x = i1;
__asm__ __volatile__ ("#dragons be here. %0" : "+r" (x));
i1 = x;
}

current mainline with -O2 -S -mtls-size=16

f3:
addi 9,2,i1@tprel
lwz 0,0(9)
#APP
#dragons be here. 0
#NO_APP
stw 0,0(9)
blr

Same thing with my modified compiler.

f3:
lwz 0,i1@tprel(2)
#APP
#dragons be here. 0
#NO_APP
stw 0,i1@tprel(2)
blr

--
Alan Modra
IBM OzLabs - Linux Technology Centre